1. Field of the Invention
This invention relates to an process for the hydrogenation of maleic acid to 1.4-butanediol and optionally gamma-butyrolactone and/or tetrahydrofuran. In this process, corrosion of process equipment (e.g. hydrogenation reactors and their internals) is minimized by the use of two hydrogenation zones and by further controlling the temperature of the first hydrogenation reaction zone such that the temperature of maleic acid in the reaction zone does not exceed about 130° C.
2. Description of the Prior Art
1,4-Butanediol is a commercial commodity with a plurality of uses. For example, 1,4-butanediol is used in the production of polybutylene terepthalate and reaction-injected molded (RIM) urethanes.
It is well known that 1,4-butanediol may be obtained by the catalytic hydrogenation of maleic acid, maleic anhydride and similar hydrogenatable compounds. In such processes, aqueous maleic acid is fed with hydrogen to a reactor containing a fixed-bed catalyst. The reaction products containing 1,4-butanediol, tetrahydrofuran and gamma-butyrolactone are then recovered and purified by conventional means.
In part, the invention relates to a two reaction-zone scheme for the production of 1,4-butanediol. U.S. Pat. No. 4,584,419 teaches a process for the hydrogenation of a di-alkyl ester to 1,4-butanediol employing two hydrogenation zones operating in sequence, where the temperature of the second zone is less than the first. U.S. Pat. No. 6,008,384 teaches a two-stage hydrogenation process for the hydrogenation of maleic acid which employs a bimetallic (Ru and Re)-on-carbon catalyst and wherein the effluent of the first-stage is cooled considerably prior to introduction into the second stage. U.S. Pat. No. 5,196,602 teaches a process for the hydrogenation of a maleic anhydride and/or maleic acid to 1,4-butanediol in a two-stage process, operated sequentially, characterized by the use of a different hydrogenation catalysts in the each hydrogenation stage.
More specifically, the invention relates to the manner in which a maleic acid feedstock is hydrogenated to 1,4-butanediol and optionally other products, so as to properly and economically contain said reactions and yield a commercially viable process. To hydrogenate maleic acid to 1 4-butanediol, an elevated temperature is required. For example, U.S. Pat. No. 6,008, 384 teaches that maleic acid is advantageously hydrogenated to 1,4-butanediol at temperatures between 160° C. and 250° C. However, at these temperatures, maleic acid has been observed to be extremely corrosive. Such conditions shorten the expected life of process equipment (e.g. hydrogenation reactors, internals and their auxiliary components), unless specialized metallurgy and/or other costly materials of construction are used. In either event, how the corrosiveness of the maleic acid is addressed in the commercial plant's design, procurement, construction, operation and maintenance has a major impact on process economics of a maleic acid to 1,4-butanediol chemical plant and hence its commercial viability.
A goal of the instant invention is a reactor system configuration and reaction temperature profile which lessens the corrosive effects of the maleic acid feedstock.